The popularity of e-cigarettes has soared in recent years, but do they pose a health risk we should be concerned about?
Many of the concerns arise from an apparent lack of evidence for the effects of e-cigarette use. As e-cigarette use is moving toward ubiquity, the gaps in knowledge about their effects are becoming more concerning for health experts.
Whether it is concerning how e-cigarettes are marketed or precisely what ingredients are contained within these devices, people are becoming wary of devices that originally appeared to be completely benign.
In a study of American adults published in Nicotine and Tobacco Research last year, 37% were opposed to e-cigarette use in smoke-free areas, with around 40% uncertain. This finding suggests both caution and uncertainty regarding the safety of e-cigarettes.
For this Spotlight feature, we take a look at what the apparent dangers associated with e-cigarette use are, aiming to assess just how worried, if at all, we should be about e-cigarettes.
E-cigarettes and their regulation
So what precisely are e-cigarettes comprised of that could make them dangerous? The majority of devices have a mouthpiece or cartridge, an atomizer and a battery. The cartridge holds a liquid solution (usually containing nicotine) that is heated up and vaporized by the atomizer. Once the liquid is vaporized, the user can inhale it, mimicking the process of smoking.
The solutions within the cartridges have variable concentrations of nicotine - amounts can range from no nicotine at all to high concentrations (24-36 mg/ml).
A report from the Centers for Disease Control and Prevention (CDC) published last year revealed that e-cigarette-related calls to poison centers in the US increased dramatically over the past 5 years. In 2010, there was one call per month, but this rose to around 215 calls per month by 2014.
Does this increase signal a dangerous toxicity in e-cigarettes? Dr. Tom Frieden, director of the CDC, stated that the report "raises another red flag about e-cigarettes: the liquid nicotine used in e-cigarettes can be hazardous."
Defenders of the device could point to how these poisonings occurred. More than half of the calls to poison centers involved children aged 5 years and under, suggesting that misuse of a product intended for adults was to blame.
E-cigarettes consist of cartridges, atomizers and power sources. There have been some concerns about health risks posed by the cartridges and the liquid solutions they contain.
According to the investigators, however, child poisoning was usually due to the direct contact with the cartridge liquid, either through ingestion, inhalation or exposure to the liquid on their skin or eyes.
"Use of these products is skyrocketing and these poisonings will continue," says Dr. Frieden. "E-cigarette liquids as currently sold are a threat to small children because they are not required to be childproof, and they come in candy and fruit flavors that are appealing to children."
The fact that e-cigarettes are not required to be childproof comes from their position in a regulatory gray area. At present, the US Food and Drug Administration (FDA) can only regulate e-cigarettes that manufacturers market as therapeutic, giving those who choose not to market their products this way more freedom to construct them as they please.
Last year, the FDA announced a proposal to extend current tobacco regulation to include all e-cigarettes and other products that meet the legal definition of a tobacco product. This would allow them to restrict the way e-cigarettes are advertised and promoted, especially campaigns designed to appeal to youths.
Until this proposed rule is finalized, the aspects of e-cigarette presentation that Dr. Frieden is most concerned about are likely to continue. Consumers will also have to wait for an accepted set of measures to confirm the purity of e-cigarettes and the liquids used within.
Substances in e-cigarettes
In terms of the chemicals contained in e-cigarettes, much is still unknown about precisely what is present and what their long-term effects are. While manufacturers will claim that their devices are safe, various studies have questioned this presumption.
The FDA themselves analyzed samples of two popular brands of e-cigarette. The investigators found variable levels of nicotine - perhaps not so much of a surprise - but also identified traces of toxic chemicals including carcinogens, substances known to cause cancer. Examples of these chemicals include formaldehyde and acetaldehyde.
After making these findings, the FDA issued a warning about the potential dangers of using e-cigarettes.
A study conducted by researchers from the University of Southern California found that the vapor produced by a popular brand of e-cigarette contained toxic levels of certain metals far greater than those found in the smoke of traditional cigarettes.
"Our results demonstrate that overall, electronic cigarettes seem to be less harmful than regular cigarettes, but their elevated content of toxic metals such as nickel and chromium do raise concerns," says Prof. Sioutas, coauthor of the study.
The researchers believe that these metal particles, mainly chromium and nickel, were likely to have come from the e-cigarette cartridges, suggesting that better manufacturing standards for the devices may be required.
Another study, published earlier this year in PLOS ONE, found that e-cigarette exposure could impair the antimicrobial defenses of the lungs in a mouse model.
This study has been criticized for only comparing the consequences of e-cigarette use with fresh air and not with smoking, as well as for using mice, known to be affected differently by nicotine than humans. However, the researchers state that their findings merely serve to illustrate a need for further testing before e-cigarettes can be portrayed as a safe alternative to traditional smoking.
Finally, researchers have also pointed out the dangers of nicotine, which is found in the majority of e-cigarettes. A study published last year in Oncotarget found that nicotine exposure caused cells to mutate in a manner similar to oxidative stress, a precursor to cancer.
The authors concluded that exposure to nicotine over a long period could lead to mutated genes that increase an individual's likelihood of developing cancer, even though nicotine itself is not yet considered to be carcinogenic.
Although e-cigarettes do not contain some of the most harmful substances found in traditional cigarettes - tobacco, tar and the chemicals produced by burning tobacco - and are, therefore, safer to use, there is evidence to suggest that e-cigarettes should not be viewed as being without risk.
On the next page we examine whether e-cigarettes are a smoking cessation aid or a gateway to tobacco. We also discuss the lack of robust evidence on e-cigarettes.